You have the same problem with Steam already for years.. I mean you do not have a physical copy anymore. In fact if Steam is down, you might not be able to download, play or play multiplayer. So you own nothing and be happy - WEF.
Steam is different, though; many games have no DRM and even more just have Steam's DRM that's already been cracked globally and is super quick to patch. They also maintain access to paid games even after they're delisted.
AFAIK, the only problems with maintaining access to Stream games are software-as-a-service games when servers go down (MMOs and multiplayer servers, basically) and music with expired licenses (fuck the RIAA and copyright law for that one; not much Steam can do about that.) I have many delisted games in my library and I can download them any time I want.
Sure, Steam could go down, at some point. Maybe. But it's not a big concern.
Nope.. Some games will fail to start if the "main" server is down or some authentication server or whatever server it nowadays might depend on. So even if you install a game now and let it rest of years, the changes it will start again over 10 years is very low. I'm not even talking about multiplayer, since multiplayer will be definitively broken by then. And LAN features are no longer implemented by game devs.
I do agree that gamepass will only make matters worse.